It is known in the art to focus a broadband beam of electromagnetic radiation onto a small spot in ellipsometers by reflective or refractive optics. Typically, said prior art systems image a small aperture onto a spot on a sample with high demagnification, and suffer from varying degrees of optical aberrations, (eg. spherical, chromatic, astigmatism etc.). Further, surfaces of mirrors can be non-ideal as a result of non-traditional manufacturing of special optics. Further, the cost of non-spherical optics is high.
It is also known that spherical optics can be fashioned to relay an objective with 1:1 magnification and with essentially no aberrations. Expired U.S. Pat. No. 3,748,015 describes such a relay system comprising two elements:                a) a concave spherical mirror; and        c) a convex spherical mirror;said elements being arrange such that electromagnetic radiation caused to approach the concave spherical reflects at a first location thereon is reflected to said a convex spherical mirror, from which it reflects onto a second location of said concave spherical mirror, from which it reflects as a converging beam of electromagnetic radiation if the electromagnetic radiation caused to approach the concave spherical mirror at a first location was, for instance, a point source. FIG. 1 of this disclosure demonstrates a 015 Patent System.        
Patents which describe reflective optics in ellipsometer systems are U.S. Pat. Nos. 6,734,967; 5,910,842 and 5,608,526 to Piwonka-Corle et al. The 526 Patent is the earliest thereof to describe use of all-reflective focusing elements in an ellipsometer. Patents to Norton, U.S. Pat. Nos. 5,859,424 and 5,917,594 are disclosed as they describe use of an apodizing filter to decrease beam spot size on a sample, and use of a negative miniscus lens to correct for spherical abberations where a spherical mirror is present in the path of an electromagnetic beam.
The disclosed invention applies the system of the expired 015 Patent in reflectometer, spectrophotometer, ellipsometer, polarimeter and the like systems, variously combined with spatial filters.